src/libsyntax/feature_gate.rs

   1 // Copyright 2013 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Feature gating
  12 //!
  13 //! This modules implements the gating necessary for preventing certain compiler
  14 //! features from being used by default. This module will crawl a pre-expanded
  15 //! AST to ensure that there are no features which are used that are not
  16 //! enabled.
  17 //!
  18 //! Features are enabled in programs via the crate-level attributes of
  19 //! `#![feature(...)]` with a comma-separated list of features.
  20 use self::Status::*;
  21
  22 use abi::RustIntrinsic;
  23 use ast::NodeId;
  24 use ast;
  25 use attr;
  26 use attr::AttrMetaMethods;
  27 use codemap::{CodeMap, Span};
  28 use diagnostic::SpanHandler;
  29 use visit;
  30 use visit::Visitor;
  31 use parse::token;
  32
  33 use std::slice;
  34 use std::ascii::AsciiExt;
  35
  36
  37 // if you change this list without updating src/doc/reference.md, @cmr will be sad
  38 static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[
  39     ("globs", Accepted),
  40     ("macro_rules", Accepted),
  41     ("struct_variant", Accepted),
  42     ("asm", Active),
  43     ("managed_boxes", Removed),
  44     ("non_ascii_idents", Active),
  45     ("thread_local", Active),
  46     ("link_args", Active),
  47     ("phase", Removed),
  48     ("plugin_registrar", Active),
  49     ("log_syntax", Active),
  50     ("trace_macros", Active),
  51     ("concat_idents", Active),
  52     ("unsafe_destructor", Active),
  53     ("intrinsics", Active),
  54     ("lang_items", Active),
  55
  56     ("simd", Active),
  57     ("default_type_params", Accepted),
  58     ("quote", Active),
  59     ("link_llvm_intrinsics", Active),
  60     ("linkage", Active),
  61     ("struct_inherit", Removed),
  62
  63     ("quad_precision_float", Removed),
  64
  65     ("rustc_diagnostic_macros", Active),
  66     ("unboxed_closures", Active),
  67     ("import_shadowing", Active),
  68     ("advanced_slice_patterns", Active),
  69     ("tuple_indexing", Accepted),
  70     ("associated_types", Accepted),
  71     ("visible_private_types", Active),
  72     ("slicing_syntax", Active),
  73
  74     ("if_let", Accepted),
  75     ("while_let", Accepted),
  76
  77     ("plugin", Active),
  78
  79     // A temporary feature gate used to enable parser extensions needed
  80     // to bootstrap fix for #5723.
  81     ("issue_5723_bootstrap", Accepted),
  82
  83     // A way to temporarily opt out of opt in copy. This will *never* be accepted.
  84     ("opt_out_copy", Deprecated),
  85
  86     // A way to temporarily opt out of the new orphan rules. This will *never* be accepted.
  87     ("old_orphan_check", Deprecated),
  88
  89     // A way to temporarily opt out of the new impl rules. This will *never* be accepted.
  90     ("old_impl_check", Deprecated),
  91
  92     // OIBIT specific features
  93     ("optin_builtin_traits", Active),
  94
  95     // These are used to test this portion of the compiler, they don't actually
  96     // mean anything
  97     ("test_accepted_feature", Accepted),
  98     ("test_removed_feature", Removed),
  99 ];
 100
 101 enum Status {
 102     /// Represents an active feature that is currently being implemented or
 103     /// currently being considered for addition/removal.
 104     Active,
 105
 106     /// Represents a feature gate that is temporarily enabling deprecated behavior.
 107     /// This gate will never be accepted.
 108     Deprecated,
 109
 110     /// Represents a feature which has since been removed (it was once Active)
 111     Removed,
 112
 113     /// This language feature has since been Accepted (it was once Active)
 114     Accepted,
 115 }
 116
 117 /// A set of features to be used by later passes.
 118 #[derive(Copy)]
 119 pub struct Features {
 120     pub unboxed_closures: bool,
 121     pub rustc_diagnostic_macros: bool,
 122     pub import_shadowing: bool,
 123     pub visible_private_types: bool,
 124     pub quote: bool,
 125     pub opt_out_copy: bool,
 126     pub old_orphan_check: bool,
 127 }
 128
 129 impl Features {
 130     pub fn new() -> Features {
 131         Features {
 132             unboxed_closures: false,
 133             rustc_diagnostic_macros: false,
 134             import_shadowing: false,
 135             visible_private_types: false,
 136             quote: false,
 137             opt_out_copy: false,
 138             old_orphan_check: false,
 139         }
 140     }
 141 }
 142
 143 struct Context<'a> {
 144     features: Vec<&'static str>,
 145     span_handler: &'a SpanHandler,
 146     cm: &'a CodeMap,
 147 }
 148
 149 impl<'a> Context<'a> {
 150     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 151         if !self.has_feature(feature) {
 152             self.span_handler.span_err(span, explain);
 153             self.span_handler.span_help(span, format!("add #![feature({})] to the \
 154                                                        crate attributes to enable",
 155                                                       feature).index(&FullRange));
 156         }
 157     }
 158
 159     fn has_feature(&self, feature: &str) -> bool {
 160         self.features.iter().any(|&n| n == feature)
 161     }
 162 }
 163
 164 struct MacroVisitor<'a> {
 165     context: &'a Context<'a>
 166 }
 167
 168 impl<'a, 'v> Visitor<'v> for MacroVisitor<'a> {
 169     fn visit_mac(&mut self, mac: &ast::Mac) {
 170         let ast::MacInvocTT(ref path, _, _) = mac.node;
 171         let id = path.segments.last().unwrap().identifier;
 172
 173         if id == token::str_to_ident("asm") {
 174             self.context.gate_feature("asm", path.span, "inline assembly is not \
 175                 stable enough for use and is subject to change");
 176         }
 177
 178         else if id == token::str_to_ident("log_syntax") {
 179             self.context.gate_feature("log_syntax", path.span, "`log_syntax!` is not \
 180                 stable enough for use and is subject to change");
 181         }
 182
 183         else if id == token::str_to_ident("trace_macros") {
 184             self.context.gate_feature("trace_macros", path.span, "`trace_macros` is not \
 185                 stable enough for use and is subject to change");
 186         }
 187
 188         else if id == token::str_to_ident("concat_idents") {
 189             self.context.gate_feature("concat_idents", path.span, "`concat_idents` is not \
 190                 stable enough for use and is subject to change");
 191         }
 192     }
 193 }
 194
 195 struct PostExpansionVisitor<'a> {
 196     context: &'a Context<'a>
 197 }
 198
 199 impl<'a> PostExpansionVisitor<'a> {
 200     fn gate_feature(&self, feature: &str, span: Span, explain: &str) {
 201         if !self.context.cm.span_is_internal(span) {
 202             self.context.gate_feature(feature, span, explain)
 203         }
 204     }
 205 }
 206
 207 impl<'a, 'v> Visitor<'v> for PostExpansionVisitor<'a> {
 208     fn visit_name(&mut self, sp: Span, name: ast::Name) {
 209         if !token::get_name(name).get().is_ascii() {
 210             self.gate_feature("non_ascii_idents", sp,
 211                               "non-ascii idents are not fully supported.");
 212         }
 213     }
 214
 215     fn visit_view_item(&mut self, i: &ast::ViewItem) {
 216         match i.node {
 217             ast::ViewItemUse(..) => {}
 218             ast::ViewItemExternCrate(..) => {
 219                 for attr in i.attrs.iter() {
 220                     if attr.check_name("plugin") {
 221                         self.gate_feature("plugin", attr.span,
 222                                           "compiler plugins are experimental \
 223                                            and possibly buggy");
 224                     }
 225                 }
 226             }
 227         }
 228         visit::walk_view_item(self, i)
 229     }
 230
 231     fn visit_item(&mut self, i: &ast::Item) {
 232         for attr in i.attrs.iter() {
 233             if attr.name() == "thread_local" {
 234                 self.gate_feature("thread_local", i.span,
 235                                   "`#[thread_local]` is an experimental feature, and does not \
 236                                   currently handle destructors. There is no corresponding \
 237                                   `#[task_local]` mapping to the task model");
 238             } else if attr.name() == "linkage" {
 239                 self.gate_feature("linkage", i.span,
 240                                   "the `linkage` attribute is experimental \
 241                                    and not portable across platforms")
 242             }
 243         }
 244         match i.node {
 245             ast::ItemForeignMod(ref foreign_module) => {
 246                 if attr::contains_name(i.attrs.index(&FullRange), "link_args") {
 247                     self.gate_feature("link_args", i.span,
 248                                       "the `link_args` attribute is not portable \
 249                                        across platforms, it is recommended to \
 250                                        use `#[link(name = \"foo\")]` instead")
 251                 }
 252                 if foreign_module.abi == RustIntrinsic {
 253                     self.gate_feature("intrinsics",
 254                                       i.span,
 255                                       "intrinsics are subject to change")
 256                 }
 257             }
 258
 259             ast::ItemFn(..) => {
 260                 if attr::contains_name(i.attrs.index(&FullRange), "plugin_registrar") {
 261                     self.gate_feature("plugin_registrar", i.span,
 262                                       "compiler plugins are experimental and possibly buggy");
 263                 }
 264             }
 265
 266             ast::ItemStruct(..) => {
 267                 if attr::contains_name(i.attrs.index(&FullRange), "simd") {
 268                     self.gate_feature("simd", i.span,
 269                                       "SIMD types are experimental and possibly buggy");
 270                 }
 271             }
 272
 273             ast::ItemImpl(_, polarity, _, _, _, _) => {
 274                 match polarity {
 275                     ast::ImplPolarity::Negative => {
 276                         self.gate_feature("optin_builtin_traits",
 277                                           i.span,
 278                                           "negative trait bounds are not yet fully implemented; \
 279                                           use marker types for now");
 280                     },
 281                     _ => {}
 282                 }
 283
 284                 if attr::contains_name(i.attrs.as_slice(),
 285                                        "unsafe_destructor") {
 286                     self.gate_feature("unsafe_destructor",
 287                                       i.span,
 288                                       "`#[unsafe_destructor]` allows too \
 289                                        many unsafe patterns and may be \
 290                                        removed in the future");
 291                 }
 292
 293                 if attr::contains_name(i.attrs.index(&FullRange),
 294                                        "old_orphan_check") {
 295                     self.gate_feature(
 296                         "old_orphan_check",
 297                         i.span,
 298                         "the new orphan check rules will eventually be strictly enforced");
 299                 }
 300
 301                 if attr::contains_name(i.attrs.index(&FullRange),
 302                                        "old_impl_check") {
 303                     self.gate_feature("old_impl_check",
 304                                       i.span,
 305                                       "`#[old_impl_check]` will be removed in the future");
 306                 }
 307             }
 308
 309             _ => {}
 310         }
 311
 312         visit::walk_item(self, i);
 313     }
 314
 315     fn visit_foreign_item(&mut self, i: &ast::ForeignItem) {
 316         if attr::contains_name(i.attrs.index(&FullRange), "linkage") {
 317             self.gate_feature("linkage", i.span,
 318                               "the `linkage` attribute is experimental \
 319                                and not portable across platforms")
 320         }
 321
 322         let links_to_llvm = match attr::first_attr_value_str_by_name(i.attrs.as_slice(),
 323                                                                      "link_name") {
 324             Some(val) => val.get().starts_with("llvm."),
 325             _ => false
 326         };
 327         if links_to_llvm {
 328             self.gate_feature("link_llvm_intrinsics", i.span,
 329                               "linking to LLVM intrinsics is experimental");
 330         }
 331
 332         visit::walk_foreign_item(self, i)
 333     }
 334
 335     fn visit_ty(&mut self, t: &ast::Ty) {
 336         visit::walk_ty(self, t);
 337     }
 338
 339     fn visit_expr(&mut self, e: &ast::Expr) {
 340         match e.node {
 341             ast::ExprRange(..) => {
 342                 self.gate_feature("slicing_syntax",
 343                                   e.span,
 344                                   "range syntax is experimental");
 345             }
 346             _ => {}
 347         }
 348         visit::walk_expr(self, e);
 349     }
 350
 351     fn visit_attribute(&mut self, attr: &ast::Attribute) {
 352         if attr::contains_name(slice::ref_slice(attr), "lang") {
 353             self.gate_feature("lang_items",
 354                               attr.span,
 355                               "language items are subject to change");
 356         }
 357     }
 358
 359     fn visit_pat(&mut self, pattern: &ast::Pat) {
 360         match pattern.node {
 361             ast::PatVec(_, Some(_), ref last) if !last.is_empty() => {
 362                 self.gate_feature("advanced_slice_patterns",
 363                                   pattern.span,
 364                                   "multiple-element slice matches anywhere \
 365                                    but at the end of a slice (e.g. \
 366                                    `[0, ..xs, 0]` are experimental")
 367             }
 368             _ => {}
 369         }
 370         visit::walk_pat(self, pattern)
 371     }
 372
 373     fn visit_fn(&mut self,
 374                 fn_kind: visit::FnKind<'v>,
 375                 fn_decl: &'v ast::FnDecl,
 376                 block: &'v ast::Block,
 377                 span: Span,
 378                 _node_id: NodeId) {
 379         match fn_kind {
 380             visit::FkItemFn(_, _, _, abi) if abi == RustIntrinsic => {
 381                 self.gate_feature("intrinsics",
 382                                   span,
 383                                   "intrinsics are subject to change")
 384             }
 385             _ => {}
 386         }
 387         visit::walk_fn(self, fn_kind, fn_decl, block, span);
 388     }
 389 }
 390
 391 fn check_crate_inner<F>(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate,
 392                         check: F)
 393                        -> (Features, Vec<Span>)
 394     where F: FnOnce(&mut Context, &ast::Crate)
 395 {
 396     let mut cx = Context {
 397         features: Vec::new(),
 398         span_handler: span_handler,
 399         cm: cm,
 400     };
 401
 402     let mut unknown_features = Vec::new();
 403
 404     for attr in krate.attrs.iter() {
 405         if !attr.check_name("feature") {
 406             continue
 407         }
 408
 409         match attr.meta_item_list() {
 410             None => {
 411                 span_handler.span_err(attr.span, "malformed feature attribute, \
 412                                                   expected #![feature(...)]");
 413             }
 414             Some(list) => {
 415                 for mi in list.iter() {
 416                     let name = match mi.node {
 417                         ast::MetaWord(ref word) => (*word).clone(),
 418                         _ => {
 419                             span_handler.span_err(mi.span,
 420                                                   "malformed feature, expected just \
 421                                                    one word");
 422                             continue
 423                         }
 424                     };
 425                     match KNOWN_FEATURES.iter()
 426                                         .find(|& &(n, _)| name == n) {
 427                         Some(&(name, Active)) => {
 428                             cx.features.push(name);
 429                         }
 430                         Some(&(name, Deprecated)) => {
 431                             cx.features.push(name);
 432                             span_handler.span_warn(
 433                                 mi.span,
 434                                 "feature is deprecated and will only be available \
 435                                  for a limited time, please rewrite code that relies on it");
 436                         }
 437                         Some(&(_, Removed)) => {
 438                             span_handler.span_err(mi.span, "feature has been removed");
 439                         }
 440                         Some(&(_, Accepted)) => {
 441                             span_handler.span_warn(mi.span, "feature has been added to Rust, \
 442                                                              directive not necessary");
 443                         }
 444                         None => {
 445                             unknown_features.push(mi.span);
 446                         }
 447                     }
 448                 }
 449             }
 450         }
 451     }
 452
 453     check(&mut cx, krate);
 454
 455     (Features {
 456         unboxed_closures: cx.has_feature("unboxed_closures"),
 457         rustc_diagnostic_macros: cx.has_feature("rustc_diagnostic_macros"),
 458         import_shadowing: cx.has_feature("import_shadowing"),
 459         visible_private_types: cx.has_feature("visible_private_types"),
 460         quote: cx.has_feature("quote"),
 461         opt_out_copy: cx.has_feature("opt_out_copy"),
 462         old_orphan_check: cx.has_feature("old_orphan_check"),
 463     },
 464     unknown_features)
 465 }
 466
 467 pub fn check_crate_macros(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 468 -> (Features, Vec<Span>) {
 469     check_crate_inner(cm, span_handler, krate,
 470                       |ctx, krate| visit::walk_crate(&mut MacroVisitor { context: ctx }, krate))
 471 }
 472
 473 pub fn check_crate(cm: &CodeMap, span_handler: &SpanHandler, krate: &ast::Crate)
 474 -> (Features, Vec<Span>) {
 475     check_crate_inner(cm, span_handler, krate,
 476                       |ctx, krate| visit::walk_crate(&mut PostExpansionVisitor { context: ctx },
 477                                                      krate))
 478 }